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>> Tuesday, February 22, 2011

A.Introduction/Background

Some B727 operator has experienced flight delay due to some A/P component terminals located in E&E bay rack found shorted. Further assessment revealed water has entered cargo area from wet loads at various times, passed through the cargo floor via defective/damaged sealant and accumulated in the area of the terminal strips. In the present case, with sufficient accumulation, it has shorted various terminals, and this has caused the burning in the roll channel. Fig 1 thru 4 shows dripped water from main deck accumulated in electronic rack.

B.Reason for Study

This study reviews the practical long term preventive actions to prevent water originated from wet bulk cargo in main cargo position A and B to spill into E&E compartment and affect any black box connectors.

2.Drained water/liquid from main deck will be trapped in these covers and guided thru the outboard fuselage skin and therefore discharged via drain hole located in the most bottom of fuselage belly BL0.

3.Auto pilot component terminal strips which were found corroded and shorted due to water contamination are located just below BS380 floor beam.

4.Water protection cover P/N 65-69360-2 was found installed on the dedicated area between BS380 and BS400. However, excessive water from the main deck was uncontrolled since fwd end of this water protection cover is free end which water may drip downward thus accumulated on the terminal strip mounting.

5.Water is originated from wet bulk cargo loading especially during rainy day and drop into main cargo deck floor. Hence, prevention must be taken to avoid it’s from slips into the gap between floor board joints and attachment screws in the first place.

6.Boeing message #1-780460211-2 recommends use of Hi-Tak tape in between floor board lower surface common to floor beam attachment as per Service Letter 737-SL-53-078 or -066. Although this SL provides solutions for 737 main deck floor beam upper surface corrosion due to water/liquid, they serves as water ingress from the floor board downward prevention as well.

7.Possibility of installation new composite panel which serves as drip pan on the E&E compartment ceiling has also been considered. Fabrication of the panel to meet flammability requirement is not an issue. However, installation wise to the surrounding aircraft structure was concerned most. Altering structure configuration requires complicated analysis and quite expensive cost may be required if any Structural Significant Item (SSI) affected by the modification.

D.Recommendations

1.)Accomplish modification to install Hi-Tak tape in between main deck floor panel and their attachments to floor beam from BS344 to BS460 (E&E bay area) i.a.w 737-SL-53-078. This mod also reduces possibility of corrosion initiate on the floor beam due to water/liquid contamination.

2.)Entire fleet inspection to ensure all water protection cover panels installed in specific area. Any area on inspected aircraft found no cover protection must be restored per IPC with immediate effect.

E.Conclusion

Major factor caused the incident was identified due to improper sealing of the main deck floor panel to the floor beams, especially in position A and B area where E&E bay was located underneath. Accomplishment of proposed mod per para D 1 would avoid water from wet cargo to ingress into E&E bay thus reduce the possibility electric/electrical terminal strips shorted with minimum cost.